This invention relates to a new and improved process for preparing guar gum, especially finely divided, high viscosity guar gum.
Guar gum has diverse industrial uses including its use as a thickener and/or stabilizer in the textile, food, cosmetic and pharmaceutical industries. It is also used as a beater additive for paper and as a fluid loss control agent and flocculant in oil well drilling muds.
As used herein the term "guar gum," often called guar flour after grinding, refers to the mucilage found in the seed of the leguminous plant Cyamopsis tetragonoloba. Guar seeds are composed of a pair of tough, non-brittle endosperm sections, hereafter referred to as "guar splits," between which is sandwiched the brittle embryo (germ). The entire structure is enclosed in a tough seedcoat (hull) (14-17% of the seed) which is generally removed by passing the seeds rapidly through heat and then subjecting them to a pearling operation, wherein the components of the seed are separated by multi-stage grinding and sifting operations. After dehulling, the seeds are split, the germ (43-47% of the seed) is removed by screening, and the splits are ground to provide the gum. The gum is present in the splits contained in tiny cells having a water-insoluble cell wall. The gum in these cells is rather slowly dispersible in water, and accordingly it is desirable to disrupt the cell wall as well as to obtain a fine particle size.
The splits are reported to contain about 78-82% galactomannan polysaccharide and minor amounts of some proteinaceous material, inorganic salts, water-insoluble gum, and cell membranes, as well as some residual seedcoat and embryo. They are tough and extremely difficult to grind. Hence, several wet milling and extraction processes have been suggested for the recovery of the gum from the splits.
U.S. Pat. No. 2,891,050 describes one such process which involves tempering (hydrating) guar splits until they have a moisture content of 30-60% by weight of water, flattening (flaking) the wet splits into thin flakes by passing them between rolls, and then drying and grinding them. The flakes may be ground prior to drying or may be used without grinding.
U.S. Pat. No. 3,455,899 describes a process for producing a low odor, low taste galactomannan gum by treating the splits with steam at about 90.degree.-100.degree. C. for up to 1 hour after the splits have reached the temperature of the steam. The splits are subsequently tempered, flattened, dried, and ground. The steam treatment may be conducted simultaneously with the tempering.
British Pat. No. 906,327 describes a process for extracting galactomannan polysaccharide from guar seeds, preferably the guar seed flakes obtained by crushing the seeds. The flakes or seeds are subjected to the action of an aqueous caustic alkali at 60.degree.-120.degree. C. in the presence of a salt which retards swelling of the polysaccharide. The gum may be separated by centrifugation.
Another extraction process is described in an article entitled "Mannose-Containing Polysaccharides: A Method for The Extraction and Estimation of Gum of Guar (Cyamopsis tetragonolba L. Taub)" by K. C. Sikka and R. P. Johari (Research and Industry, Vol 14, pp. 138-139, July-Sept. 1969). Seed endosperm, previously ground to pass a 40 mesh sieve, is extracted with water at 70.degree.-80.degree. C. for 30 minutes and the solids are separated from the extract by centrifuging. The supernatant extract obtained after repeated extraction and centrifugation is poured into ethanol to precipitate the gum.
The above processes generally do not give the desired high viscosity guar gum. Hence, it is an object of this invention to provide a rapid, facile process which will produce guar gum, especially a finely divided, high viscosity guar gum.